In recent years, consumption of fats has been increasing every year in Japan with westernization of lifestyles including eating habits. It is known that fats excessively taken up are gradually accumulated in bodies, and become factors of inducing various diseases. Mechanisms of the fat accumulation is roughly classified into the following two classes. According to one of the mechanisms, excessive fats existing in blood deposit on blood vessel walls, which leads to stenosis of blood vessels to gradually develops into arteriosclerosis, and some time later triggers the onset of myocardial infarction, angina pectoris, cerebral infarction, and the like. According to the other mechanism, excessive fats similarly deposit in visceral organs. In particular, so-called hepatic steatosis, in which a lot of fats deposit in the liver, has recently been frequently observed, and some of hepatic steatosis advance at some future to non-alcoholic steatohepatitis, cirrhosis, and hepatoma (Gastroenterology, 116, 1413-1419 (1999)). The aforementioned diseases are based on the different onset mechanisms, and accordingly, a medicament suitable for prophylactic and/or therapeutic treatment of each disease is needed.
As a therapeutic agent of hepatic steatosis, polyenephosphatidylcholine has been clinically used. Further, fibrate agents, of which typical examples include clofibrate as an antihyperlipidemic agent, have also been clinically used as therapeutic agents for hepatic steatosis. It is considered that the fibrate agents improve lipid metabolism by acting on enzymes for fatty acid β-oxidation system in the liver (Ann. N.Y. Acad. Sci., 386, 111-135 (1982)). However, side reactions such as liver function failure are generally known for the fibrate agents (Atherosclerosis, 92, 31-40 (1992)), and therefore a medicament for prophylactic and/or therapeutic treatment of hepatic steatosis or non-alcoholic steatohepatitis with less side effects has been desired.
(2E,4E,6E,10E)-3,7,11,15-Tetramethyl-2,4,6,10,14-hexadecapentaenoic acid, which is one of polyprenyl compounds and has a chemical structure totally different from those of polyenephosphatidylcholine and the fibrate agents mentioned above, is a acyclic retinoid having affinity for retinoic acid binding proteins and retinoic acid receptors, and actions thereof for inducing differentiation and inducing apoptosis in hepatocellular carcinoma are known. Clinically, (2E,4E,6E,10E)-3,7,11,15-tetramethyl-2,4,6,10,14-hexadecapentaenoic acid significantly inhibited recurrence of hepatoma after radical treatment thereof by long-term administration for one year, and thus suppressing action thereof on the recurrence of hepatoma was suggested. Further, liver function failure or other adverse effects, those caused by retinoids, were not substantially observed during the administration thereof, and therefore the compound was revealed to be a safe medicament (N. Eng. J. Med., 334, 1561-1567 (1996)).
However, it was not known that polyprenyl compounds had prophylactic and therapeutic effectiveness on hepatic steatosis or non-alcoholic steatohepatitis.    Non-patent document 1: Gastroenterology, 116, pp. 1413-1419 (1999)    Non-patent document 2:Ann. N.Y. Acad. Sci., 386, pp. 111-135 (1982)    Non-patent document 3:Atherosclerosis, 92, pp. 31-40 (1992)    Non-patent document 4: N. Eng. J. Med., 334, pp. 1561-1567 (1996)